LGT Switch LED Hack?

I seem to recall reading that LGT do some very crude hack which turns on their switch LEDs with the blade but doesn’t use an LED pad or accent config. Can anyone remember what it is, as I don’t have an LGT hilt to check it?

The reason I ask is I’m swapping out a broken CFX for a Proffie for a customer. The hilt is hard to open but I can access the board to do the swap but can’t reach the back of the switches. The trouble is the switch LED has a common ground with the Main and Aux switch negs, because the CFX accent LED pads are designed for common neg with individual positives (opposite to Proffie).

So I need a pad that switches the positive on and off with the blade and I can then wire the switch LED positive to that.

I seem recall LGT use a speaker pad, but I could be wrong. Is there another pad that would do this job?

It occurred to me to send the switch + to battery + and the switch common neg to a FET, then set the FET to a pixel blade but to always black. My understanding is this would leave the FET connected to ground all the time as long as I didn’t use the idle off time define. But my gut tells me this would run down the battery quicker as this hilt doesn’t have a kill key or kill switch.

As always, any thoughts welcome. :slight_smile:

Oh, and one last quick question for the same hilt - the CFX uses four wires for the main blade negs. For ease of wiring, I’m assuming it’s fine to use all four and wire them to four FETs on the Proffie and then just specify it in the config?

Do you know what gauge the wire is and how the emitter connector is wired?

If the switch LED can tolerate 5V (or add required resistors), you could use the 5V pad I suppose.
That only turns on when there’s sound playing and on battery power.
Yes, LGT uses a speaker pad and it flickers with the audio variances.

I’m not sure on the exact wire guage as I haven’t unsoldered the old board yet (the investigation is still in the preliminary stages! LOL!). It did occur to me to ditch one or two of the wires as they must all go to the same place. (The neo connect is an old TCSS one), but I figured loose ends would be untidy and as there are enough FETs to wire up four of them, I figured it would be OK to share the load between them. I’ve used three quite often, especially with longer blades, just not used four before.

Would the 5 volt pad interfere with the audio amplifier? I guess it can’t interfere with it as much as the speaker+ pad and LGTs don’t seem to have any issues on that score.

And flickering with audio is probably OK. As long as it lights that’s kind of all I need.

I would honestly try to take the whole thing apart and resolder the connector as well. You’re playing with unknowns.

Normally I would agree but it may be a bit destructive in this case. I figured that once I get the old board out, I can use a test meter and spare battery to trace all the wires and see what goes where to nail down polarities and stuff before I hook anything up. I wouldn’t leave anything to chance. :slight_smile:

I wouldn’t think so, especially with one small LED in a switch. I’m not the authority on that though.

I’ve heard of a single color LED positive and negative being soldered onto the blade positive and negative (with proper resisters). Basically if the blade is on the LED gets power and is turned on. Not sure if it’s LGT specifically that does that.

Quick update to this one if people are interested:

I got my test meter out and checked which pads do what and found the following:

  • The 5 volt pad output isn’t limited to when sound is playing. I tested it on an installed saber and found that it outputted 5 volts all the time, even after the idle-timeout had shut off the normal LED FETs.

  • The Speaker+ pad outputs 2.55 volts when sound is running. This appears to be irrespective of volume. This meant I was able to take a T off the speaker+ wire and run the second leg through a 47 ohm resistor to the red switch LED, which in turn shared a common ground with the switch itself.

The only slight weirdness was that I normally use a meter between the two speaker pads to check I’ve wired it right. This normally would show roughly the rated resistance of the speaker (say, 3.7 ohms for a 4 ohm speaker). However with this hack, the meter just seemed to show random milliohms numbers - the kind of thing you get when you hold the meter probes in your fingers. I can only assume this is due to the LED and resistor allowing a different path to the speaker neg which I’m guessing is related to ground.

But anyway, it works so all good.

Thanks again for your help chaps.

If that’s true, then there is a bug which should be fixed.
5v should turn off when not needed.

It’s not entirely independent of volume.
Also, it’s not actually 2.55 volts. It’s a 5 volt PWM signal running at ~400kHz.

Would this be config-related? If so I can post the config from the saber I used when I get home from work this afternoon. Thinking about it further, having a positive pad that could be referred to and controlled in the config would actually be quite useful.

That makes sense. Fortunately in this case it was good enough to achieve the desired result. :slight_smile:

It might be, having the config would be helpful in debugging the problem.
The 5v pad isn’t exactly controllable though, as there is no way to turn it off if the amplifier code or the blade code is asking for it to be on.

Here you go Prof. This is the code that was loaded onto the hilt that I tested the 5 volt pad on.
Hope it’s useful.